My First Instructables Post!

If you are skimming, my instructables pages can be found here.

If you want a small explanation and summary of the project, please, continue........  :)


For my Tangible Interactive Computing Class (838F) our final project had to include, among other things, an Instructables page on the site www.instructables.com.  The creation of this page was to replace the typical research paper that usually accompanies a term project.  The idea was to force us to create a step-by-step document of how we built our projects.  The recent explosion of open source hardware/DIY makers is fostered by such websites and blogs where people share their experiences working with hardware such as the Arduino.  

Our project (myself and Preeti Bhargava) was, to put it simply, a personal informatics black box that you clip onto your belt.  As you go about your day your activity, surrounding environment and locations are tracked to produce a report telling you how much time you spent inside and outside.  The device leverages off of a system-of-systems providing context-aware analysis for such ubiquitous computing devices.  We make sense the raw data signals from the multitude of sensors through our back-end system that uses many external API calls, home-grown context-aware systems and AI decision tree analysis. 

A brief video explanation of our project:

We in the class all agreed it would be a great idea to post something to the site vs. a research paper, but I believe we were all surprised at how receptive and supporting the community is!  Four of of the seven projects (you can view all seven here) were eventually featured on the front page of the site!  Our page currently has over 20,000 views!

So, if you haven't checked out our step-by-step process yet, please do!  It shows how the hardware was made, including the soldering involved, the 3D-printing and end product.  I hope you are somewhat inspired or excited to explore this area of DIY hardware hacking.  I know I feel empowered as a result of the projects that I contributed to in this semester-long class.  As a CS Master's/PHD student I typically took the hardware of the systems I was working with at face value.  I now know I can not only create the software that runs and extracts data from hardware but also design my own hardware and sensor systems!

I thank Dr. Jon Froehlich for that hardware liberation!

Webservice to determine if a Latitude / Longitude Point is inside a polygon or building

I spent some time trying to find an easy, do-it-yourself method to build a web-service that would take a Lat/Long as input and tell me if that point is contained within a polygon.  For my purposes I wanted to know if a point was within a building or not and a polygon will easily satisfy this request.

The Ray-casting algorithm is a method to determine just that.  Google maps and Esri have function calls that one can use within their API's, but those are client-side as you can only call such functions through javascript, JQuery or the like.  Thus if you want something on the server side you must write it yourself.

Luckily I found this rosettacode side that had the ray casting algorithm coded in several languages!  Their example uses pre-canned polygons and points.  I modified it to accept a lat/long from a user and return true if the point is within any of my polygons/buildings and false otherwise. The list of polys contain the Lat/Long points for each building.



My python code:

# Code was taken from http://rosettacode.org/wiki/Ray-casting_algorithm#Python
# uses simple ray-casting algoritm to see if point lies within a polygon
# 
# Adapted by Nick Gramsky to be used as a service to check if LatLong was inside  
#    a GIS polygon
from collections import namedtuple
from pprint import pprint as pp
import sys
 
Pt = namedtuple('Pt', 'x, y')               # Point
Edge = namedtuple('Edge', 'a, b')           # Polygon edge from a to b
Poly = namedtuple('Poly', 'name, edges')    # Polygon
 
_eps = 0.00001
_huge = sys.float_info.max
_tiny = sys.float_info.min
 
def rayintersectseg(p, edge):
    ''' takes a point p=Pt() and an edge of two endpoints a,b=Pt() of a line segment returns boolean
    '''
    a,b = edge
    if a.y > b.y:
        a,b = b,a
    if p.y == a.y or p.y == b.y:
        p = Pt(p.x, p.y + _eps)
 
    intersect = False
 
    if (p.y > b.y or p.y < a.y) or (
        p.x > max(a.x, b.x)):
        return False
 
    if p.x < min(a.x, b.x):
        intersect = True
    else:
        if abs(a.x - b.x) > _tiny:
            m_red = (b.y - a.y) / float(b.x - a.x)
        else:
            m_red = _huge
        if abs(a.x - p.x) > _tiny:
            m_blue = (p.y - a.y) / float(p.x - a.x)
        else:
            m_blue = _huge
        intersect = m_blue >= m_red
    return intersect
 
def _odd(x): return x%2 == 1
 
def ispointinside(p, poly):
    ln = len(poly)
    return _odd(sum(rayintersectseg(p, edge)
                    for edge in poly.edges ))
 
def polypp(poly):
    print "\n  Polygon(name='%s', edges=(" % poly.name
    print '   ', ',\n    '.join(str(e) for e in poly.edges) + '\n    ))'
 
if __name__ == '__main__':
    polys = [
      Poly(name='avwilliams', edges=(
        Edge(a=Pt(x=38.9913160, y=-76.937079), b=Pt(x=38.991333, y=-76.936119)),
        Edge(a=Pt(x=38.991333, y=-76.936119), b=Pt(x=38.990287, y=-76.936108)),
        Edge(a=Pt(x=38.990287, y=-76.936108), b=Pt(x=38.990278, y=-76.937057)),
        Edge(a=Pt(x=38.990278, y=-76.937057), b=Pt(x=38.990495,y=-76.937052)),
        Edge(a=Pt(x=38.990495,y=-76.937052), b=Pt(x=38.990499,y=-76.936424)),
        Edge(a=Pt(x=38.990499,y=-76.936424), b=Pt(x=38.991091,y=-76.93643)),
        Edge(a=Pt(x=38.991091,y=-76.93643), b=Pt(x=38.991104,y=-76.937079)),
        Edge(a=Pt(x=38.991104,y=-76.937079), b=Pt(x=38.9913160, y=-76.937079))
        )),
    ]  

    if len(sys.argv) != 3:
       print "Incorrect number of arguments.  Please submit a lat and a long...."

    userpoint = (Pt(x=float(sys.argv[1]), y=float(sys.argv[2])))

    testpoints = (Pt(x=float(sys.argv[1]), y=sys.argv[2]), Pt(x=38.990842, y=-76.93625),
                  Pt(x=38.9021466, y=-77), Pt(x=0, y=5),
                  Pt(x=10, y=5), Pt(x=8, y=5),
                  Pt(x=10, y=10))
 
    #print "\n TESTING WHETHER POINTS ARE WITHIN POLYGONS"
    inside = False
    for poly in polys:
        #polypp(poly)
        #print '   ', '\t'.join("%s: %s" % (p, ispointinside(p, poly))
        #                       for p in testpoints[:3])
        #if ispointinside(testpoints[1], poly):
        if ispointinside(userpoint, poly):
           inside = True

    print inside

And the corresponding php code:

Oh and this was done on a mac, hence the need to call out 'python' in the system call. Syntax for this call will vary by OS. Of course this example is using a hard-coded polygon within the python script. That's fine if you want to check only a few polygons/buildings but not a great way to code if you want to check many buildings. One could simply create a small database that stores polygons and iterate through each polygon. Using PostGres you can perform a bounds call to retrieve only polygons that contain the point within their minimin bounding rectangle and iterate through this python code. Additionally this could very well be coded in php but I just didn't have the time :) It would reduce the need to perform a system call and reduce the software dependencies....

 <PUBLIC SERVICE ANNOUNCEMENT> Yes, my php code IS very light and simple. One should ALWAYS clean user input prior to working with the parameters they provide. My example/prototype did not include that (BAD DEVELOPER) but this was an internal prototype only. </PUBLIC SERVICE ANNOUNCEMENT>